Tuberous sclerosis complex (TSC) affects 1 in 6000 individuals. TSC is an autosomal dominant inherited disorder resulting from mutations in at least two different genes, TSC1 and TSC2. Patients with TSC manifest various phenotypes associated with lesions in brain, retina, heart, kidney, lung, liver and skin. Neurological problems include epilepsy, which is present in over 80% of TSC subjects and is often medically refractory. In these patients, surgical treatment of the epilepsy is problematic because of the difficulty in differentiating epileptic brain lesions from nearby non-epileptic lesions. In our previous studies (RO1 NS38324), we found that positron emission tomography (PET) using the tracer alpha[C-11]methyl-L-tryptophan (AMT) can differentiate between epileptogenic and non-epileptogenic tubers interictally. This test has become routine in the surgical evaluation of our TSC patients and, indeed, many other epilepsy surgery centers refer their TSC patients for AMT PET scanning in Detroit. The increased AMT uptake in the epileptogenic regions of TSC reflects increased metabolism of tryptophan along the kynurenine pathway (rather than the serotonin pathway) to produce endogenous convulsants, e.g., quinolinic acid. This observation provides important clues to epileptogenesis and, therefore, a better understanding of this mechanism is important not only for TSC but also for other epileptic disorders. Aim 1 (with 3 hypotheses) was designed to provide a better understanding of the pathomechanisms associated with increased AMT uptake in epileptogenic tubers. Immunocytochemical studies will be performed to increase the understanding of tryptophan metabolism by indoleamine 2,3-dioxygenase (IDO) in TSC. One of the disadvantages of AMT PET in identifying epileptogenic tubers is that its sensitivity is only about 65%. Our preliminary data suggest that diffusion tensor imaging (DTI) measurements show differences between epileptogenic and non-epileptogenic tubers both in their connectivity patterns to subcortical structures and in their surrounding anisotropy and, when used in conjunction with AMT PET, the epileptogenic brain region can be identified in the vast majority of patients. Aim 2 (with 3 hypotheses) was designed to determine whether these DTI measures can further our understanding of the unique characteristics which differentiate epileptogenic from non-epileptogenic tubers and thus provide further localization of seizure foci in TSC subjects. Our proposed studies will provide important clinical data to improve surgical evaluation of TSC patients. Furthermore, these studies will provide important mechanistic information which will likely translate into novel pharmacological approaches for epilepsy.